Wire type corona charger for electrophotographical manufacturing of CRTs

ABSTRACT

Disclosed is a wire-type corona charger having a wire electrode disposed between ground electrode plates. The wire electrode is supported by the ends of the plurality of wire electrode supporters which are so arranged that their ends have a curvature equal to arcuately-shaped upper edge of the ground electrode plates. The curvature coincides with one of the curvatures of the horizontal axis and the vertical axis of the interior surface of the panel faceplate, while the charger is pivoted along the other curvature of the faceplate. The charger can uniformly charge the photoconductive layer and improves the charging efficiency.

FIELD OF THE INVENTION

The present invention relates to a wire-type corona charger forelectrophotographically manufacturing a screen of a CRT, and moreparticularly to a wire-type corona charger and a method using thecharger for electrophotographically manufacturing a screen of a CRT, inwhich the photoconductive layer can be uniformly charged by a wireelectrode.

BACKGROUND OF THE INVENTION

Referring to FIG. 1, a color CRT 10 generally comprises an evacuatedglass envelope consisting of a panel 12, a funnel 13 sealed to the panel12 and a tubular neck 14 connected by the funnel 13, and electron gun 11centrally mounted within the neck 14, and a shadow mask 16 removablymounted to a sidewall of the panel 12. A three-color phosphor screen isformed on the inner surface of a display window or faceplate 18 of thepanel 12.

The electron gun 11 generates three electron beams 19 a, or 19 b, saidbeams being directed along convergent paths through the shadow mask 16to the screen 20 by means of several lenses of the gun and a highpositive voltage applied through an anode button 15 and being deflectedby a deflection yoke 17 so as to scan over the screen 20 throughapertures or slits 16 a formed in the shadow mask 16.

In the color CRT 10, the phosphor screen 20, which is formed on the rearsurface of the faceplate 18, comprises an array of three phosphorelements R, G and B of three different emission colors arranged in acyclic order of a predetermined structure of multiple-stripe ormultiple-dot shape and a matrix of light absorptive material surroundingthe phosphor elements R, G and B, as shown in FIG. 2.

A thin film of aluminum 22 or an electro-conductive layer, overlying thescreen 20 in order to provide a means for applying the uniform potentialapplied through the anode button 15 to the screen 20, increases thebrightness of the phosphor screen and prevents ions in the phosphorscreen from being lost and the potential of the phosphor screen fromdecreasing. And also, a film of resin 22′such as lacquer (not shown) maybe applied between the aluminum thin film 22 and the phosphor screen 20,so as to enhance the flatness and reflectivity of the aluminum thin film22.

In a photolithographic wet process, which is well known as a prior artprocess for forming the phosphor screen, a slurry of a photosensitivebinder and phosphor particles is coated on the inner surface of thefaceplate. It does not meet the higher resolution demands and requires alot of complicated processing steps and a lot of manufacturingequipments, thereby requiring high cost in manufacturing the phosphorscreen. In addition, it discharges a large quantity of effluent such aswaste water, phosphor elements, 6th chrome sensitizer, etc., with theuse of a large quantity of clean water.

To solve or alleviate the above problems, the improved process ofelectrophotographically manufacturing the screen utilizing dry-powderedphosphor particles is developed.

U.S. Pat. No. 4,921,767, issued to Datta at al. on May 1, 1990,discloses one method of electrophotographically manufacturing thephosphor screen assembly using dry-powdered phosphor particles through aseries of steps represented in FIGS. 3A to 3E, as is briefly explainedin the following.

After the panel 12 is washed, an electro-conductive layer 32 is coatedon the faceplate 18 of the panel 12 and the photoconductive layer 34 iscoated thereon, as shown in FIG. 3A. Conventionally, theelectro-conductive layer 32 is made from an inorganic conductivematerial such as tin oxide or indium oxide, or their mixture, andpreferably, from a volatilizable organic conductive material such as apolyelectrolyte commercially known as polybrene(1,5,-dimethyl-1,5-diaza-undecamethylene polymethobromide,hexadimethrine bromide), available from Aldrich Chemical Wisc., oranother quaternary ammonium salt.

The polybrene is applied to the inner surface of the faceplate 18 in anaqueous solution containing about 10 percent by weight of propanol andbout 10 percent by weight of a water-soluble adhesion-promoting polymer(poly vinyl alcohol, polyacrylic acid, polyamides and the like), and thecoated solution is dried to form the conductive layer 32 having athickness from about 1 to 2 microns and a surface resistivity of lessthan about 10⁸ l (ohms per square unit).

The photoconductive layer 34 is formed by coating the conductive layer32 with a photoconductive solution comprising a volatilizable organicpolymeric material, a suitable photoconductive dye and a solvent. Thepolymeric material is an organic polymer such as polyvinyl carboazole,or an organic monomer such as n-ehtyl carbazole, n-vinyl carbazole ortetraphenylbutatriene dissolved in a polymeric binder such aspolymethylpolypropylene carbonate. The photoconductive compositioncontains from about 0.1 to 0.4 percent by weight such dyes as crystalviolet, chloridine blue, rhodamine EG and the like, which are sensitiveto the visible rays, preferably rays having wavelength of from about 400to 700 nm. The solvent for the photoconductive composition is an organicsuch as chlorobenzene or cyclopentanone and the like which will produceas little cross contamination as possible between the layers 32 and 34.The photoconductive layer 32 is formed to have a thickness from about 2to 6 microns.

FIG. 3B schematically illustrates a charging step, wherein thephotoconductive layer 34 overlying the electro-conductive layer 32 ispositively charged in a dark environment by a conventional positivecorona discharger 36. As shown, the charger or charging electrode of thedischarger 36 is positively applied with direct current while thenegative electrode of the discharger 36 is connected to theelectro-conductive layer 32 and grounded. The charging electrode of thedischarger 36 travels across the layer 34 and charges it with a positivevoltage in the range from −200 to +700 volt.

FIG. 3C schematically shows an exposure step, wherein the chargedphotoconductive layer 34 is exposed through a shadow mask 16 by a xenonflash lamp 35 having a lens system 35′ in the dark environment. In thisstep, the shadow mask 16 is installed on the panel 12 and theelectro-conductive layer 32 is grounded. When the xenon flash lamp 35 isswitched on to shed light on the charged photoconductive layer 34through the lens system′ and the shadow mask 16, portions of thephotoconductive layer 34 corresponding to apertures or slits 16 a of theshadow mask 16 are exposed to the light. Then, the positive charges ofthe exposed areas are discharged through the grounded conductive layer32 and the charges of the unexposed areas remain in the photoconductivelayer 34, thus establishing a latent charge image in a predeterminedarray structure, as shown in FIG. 3C. In order to exactly formlight-absorptive matrices, it is preferred that the xenon flash lamp 35travels along three positions while coinciding with three differentincident angles of the three electron beams.

FIG. 3D schematically shows a developing step which utilized adeveloping container 35″ containing dry-powdered light-absorptive orphosphor particles and carrier beads for producing static electricity bycoming into contact with the dry-powdered particles. Preferably, thecarrier beads are so mixed as to charge the light-absorptive particleswith negative electric charges and the phosphor powders with positiveelectric charges, when they come into contact with the dry-powderedparticles.

In this step, the panel 12, from which the shadow mask 16 is removed, isput on the developing container 35′ containing the dry-powderedparticles, so that the photoconductive layer 34 can come into contactwith the dry-powdered particles. In this case, the negatively chargedlight-absorptive particles are attached to the positively chargedunexposed areas of the photoconductive layer 34 by electric attraction,while the positively charged phosphor particles are repulsed by thepositively charged unexposed areas but attached by reversal developingto the exposed areas of the photoconductive layer 34 from which thepositive electric charges are discharged.

FIG. 3E schematically represents a fixing step by means of infraredradiation. In this step, the light-absorptive and phosphor particlesattached in the above developing step are fixed together and onto thephotoconductive layer 14. Therefore, the dry-powdered particles includeproper polymer components which may be melted by heat and have properadhesion.

Where the surface of the panel is flat, a conventional linear coronacharger, such as those shown and described in U.S. Pat. Nos. 3,475,169,3,515,548, and 4,386,837 issued respectively on Oct. 28, 1969, Jun. 2,1970, and Jun. 7, 1983, can be used in the above-described charging stepshown in FIG. 3B. However, where the interior surface contour of thefaceplate panel is non-planar or has a certain curvature as the usualpanel, the conventional linear charger will not uniformly charge thephotoconductive layer and may generate deleterious arcs because thespacing between the charger and the photoconductive layer cannot bemaintained uniformly.

To overcome the above problems, U.S. Pat. No. 5,132,188 disclosesanother corona discharge apparatus 36 having a corona charger 50 asshown in FIGS. 4 and 5.

Referring to FIG. 4, the corona discharge apparatus 36 includes ahousing 38 having a faceplate panel support surface 40. A faceplatepanel 12 having a conductive layer 32 and a photoconductive layer 34coated thereon, is placed upon the support surface 40 and positioned bya plurality of panel alignment members 42, which engage the outersurface of the panel sidewall. An electrical ground contact 44, attachedat one end of the housing 38, is spring biased to contact the conductivelayer 32. A corona generator 46 is disposed within the housing 38. Thegenerator 46 includes a high voltage power supply 48, which provides acorona voltage to a corona charger 50. The corona charger 50 ispivotally attached, at the center of curvature of the faceplate 12, bymeans of a support arm 52 to a support bar 54. The support arm 52 isconnected to a motor 56 by a reciprocating drive screw 58, which causesthe corona charger 50 to make multiple passes across the faceplate panel12. The ultimate charge on the photoconductive layer 34 is determined bythe number of passes across the panel which, in turn, is controlled by atimer 60 which communicates with a motor controller 62 and the highvoltage power supply 48. The charging sequence is initiated from acontrol panel 64. An electrostatic voltage probe 84, coupled to avoltmeter 86 on the control panel 64, measures the voltage on the layer34 at the end of the charging cycle. A probe driver 83 moves the probe84 into proximity with the charged photoconductive layer 34.

While only one corona charger 50 is shown in FIG. 4, multiple chargersmay be used.

The corona charger 50 is shown in FIG. 5. The corona charger comprisesan arcuately-shaped ground electrode 66 having two parallel sides 68 andan interconnecting base 70, which form a U-shaped conductor. The sides68 terminate in edges 72 that are rounded to suppress arcs duringoperation. A foil charging electrode 74 is supported, by means of aninsulator 76, between the sides 68 and the base 70 of the groundelectrode. The charging electrode 74 also is arcuately-shaped and,preferably, has a substantially arcuately-contoured edge 78 with aplurality of pin-type projections 80 extending therefrom. Thearcuately-contoured edge 78 and sides 68 are coincident with thecurvature of one axis, for example the minor axis, of the interiorsurface of the faceplate panel 12. The length of the support arm 52 isadjusted so that the center of curvature of the arc of the charger 50coincides with the center of curvature of one of the axes of the panelinterior surface.

In the means time, U.S. Pat. No. 5,519,217 issued to Wilbur, Jr. et al.,on May 21, 1996, discloses a charging apparatus having a plurality ofelectrodes or blades installed on a base over the entire interiorsurface of the faceplate 18, detailed depiction of which is omitted inthe attached drawings. In the apparatus, the focusing blades correspondto the above ground electrode, and the charging blades are disposedrespectively between the adjacent focusing blades and have a pluralityof serration formed at the ends thereof. The charging head moveslaterally within the faceplate panel by a distance substantially equalto the periodic spacing between the charging blades, thereby providing asubstantially uniform electrostatic charge to the photoconductive layeron the faceplate. Therefore, the apparatus greatly increases thecharging speed or shortens the charging time without jeopardizing theuniformity of the charge applied to the photoconductive layer, therebygreatly enhancing capability in mass production.

In order to achieve uniform exposing and developing in the steps shownin FIGS. 3C and 3D, it is preferred that the photoconductive layer 34may be uniformly charged. Further, the charging electrodes and thephotoconductive layer 34 must be prevented from being damaged by arc orspark therebetween. Therefore, the above-mentioned apparatuses employarcuately-shaped thin plates as electrodes for charging, each of theplates having a plurality of pin-type projections 80 or serration, so asto provide a stable and uniform electrostatic charge to thephotoconductive layer by means of desired corona charging.

Still, it is not easy for the pin-type projections 80 or serration tocause a uniform corona discharge due to their inherent shapes. That is,the greatest discharge is generated at the distal end of each projectionor each tooth of the serration, while the intensity of dischargedecreases as it goes far from the distal end. This problematic dischargecauses multiform exposing and developing the above exposing anddeveloping steps, thereby forming phosphor elements multiformly even ina desired array.

Meanwhile, it is well known in the art that a wire-type corona chargergenerates stable and highly uniform corona discharge and exhibitssuperior charging efficiency relative to other types of electrodes.However, because the interior surface of the panel 12 is spheric, andmoreover because the larger cathode ray tube has the more complexaspheric panel surface in which the curvature of the horizontal sectionis larger than that of the vertical section, it is not easy for the wireelectrodes to coincide with such complex curvatures.

The present invention has been made to overcome the above describedproblems, and therefore ti is an object of the present invention toprovide a wire-type corona charger for electrophotographicallymanufacturing a screen of a CRT, which can uniformly charge thephotoconductive layer by generating corona discharge through wireelectrodes.

It is another object of the present invention to provide a method forelectrophotographically manufacturing a screen of a CRT using thewire-type corona charger.

SUMMARY OF THE INVENTION

To achieve the above objects, the present invention provides a wire-typecorona charger for electrophotographically manufacturing a screen of aCRT, the wire-type corona charger being installed in a corona dischargeapparatus and pivoted with a spacing over an entire interior surface ofa panel faceplate of the screen along a first curvature which is one ofcurvatures of a horizontal axis and a vertical axis of the interiorsurface of the panel faceplate, so as to uniformly charge at leasteffective surface of a photoconductive layer with a desired voltage, thephotoconductive layer being formed on an electro-conductive layer formedon the interior surface of the panel faceplate, the wire-type coronacharger comprising:

a pair of ground electrode plates each of which has arcuately-shapedupper edge with a curvature substantially equal to a second curvature,the second curvature being a remaining one of the curvatures of thehorizontal axis and the vertical axis of the interior surface of thepanel faceplate, the pair of ground electrode plates being grounded withbeing arranged in parallel and spaced with regular intervals apart;

an insulating block disposed between the pair of the ground electrodeplates and made from electrically insulating material, the insulatingblock having a plurality of wire electrode supporters so arranged thattheir upper ends are arranged to have a curvature substantially equal tothe second curvature and lower than upper edges of the repair of groundelectrode plates; and

a wire electrode being supported by the ends of the plurality of wireelectrode supporters, to which a high voltage is applied, so that atleast effective screen of the photoconductive layer is chargeduniformly, the electro-conductive layer serving as an opposed electrodeof the wire electrode.

In accordance with another aspect of the present invention, anotherwire-type corona charger may be installed in a corona dischargeapparatus and pivoted to a predetermined distance along a firstcurvature which is one of curvatures of a horizontal axis of a verticalaxis of the interior surface of the panel faceplate, so as to uniformlycharge at least effective surface of a photoconductive layer with adesired voltage, the photoconductive layer being formed on anelectro-conductive layer formed on the interior surface of the panelfaceplate, the wire-type corona charger being pivoted with a spacingfrom the photoconductive layer, the wire-type corona charger comprising:

at least three ground electrode plates, each of which hasarcuately-shaped upper edge with a curvature substantially equal to asecond curvature, the second curvature being a remaining one of thecurvatures of the horizontal axis and the vertical axis of the interiorsurface of the panel faceplate at each section of the panel faceplatenearest to each of the ground electrodes, the pair of ground electrodeplates being grounded with being arranged in parallel and spaced withregular intervals apart;

at least two sets of insulating blocks each of which is disposedrespectively between the ground electrode plates and made fromelectrically insulating material, each of the insulating blocks having aplurality of wire electrode supporters so arranged that their upper endsare arranged to have a curvature substantially equal to the secondcurvature; and

at least two wire electrodes being supported by the upper ends of thewire electrode supporters, to which a high voltage is applied, so thatat least effective screen of the photoconductive layer is chargeduniformly, the electro-conductive layer serving as an opposed electrodeof the wire electrodes.

The present invention also provides a method for electrophotographicallymanufacturing a screen of a CRT, the method comprising the steps of:

(1) firstly coating an inner surface of a panel faceplate to form avolatile conductive layer on the inner surface;

(2) secondly coating the volatile conductive layer with aphotoconductive solution to form a volatile photoconductive layer on thevolatile conductive layer, the photoconductive solution notcontaminating the volatile conductive layer;

(3) charging at least effective surface of the volatile photoconductivelayer with uniform electrostatic charges by pivoting a wire-type coronacharger along a first curvature corresponding to one of the curvaturesof the horizontal axis and the vertical axis of an interior surface ofthe panel faceplate with a spacing over an entire interior surface ofthe panel faceplate, the corona charger generating a corona discharge;

(4) exposing the volatile photoconductive layer through a shadow mask toa light according to a characteristic of the volatile photoconductivelayer, so as to selectively discharge the electrostatic charges havingbeen charged on the volatile photoconductive layer in step 3; and

(5) developing the photoconductive layer by attaching powdered particleson one of an exposed area and an unexposed area of the photoconductivelayer after charging the powdered particles, the exposed area havingbeen exposed to light in step 4 to lose the electrostatic charges,wherein the wire-type corona charger comprises:

a pair of ground electrode plates each of which has arcuately-shapedupper edge with a curvature substantially equal to a second curvature,the second curvature being a remaining one of the curvatures of thehorizontal axis and the vertical axis of the interior surface of thepanel faceplate, the pair of ground electrode plates being grounded withbeing arranged in parallel and spaced with regular intervals apart;

an insulating block disposed between the pair of the ground electrodeplates and made from electrically insulating material, the insulatingblock having a plurality of wire electrode supporters so arranged thattheir upper ends are arranged to have a curvature substantially equal tothe second curvature and lower than upper edges of the pair of groundelectrode plates; and

a wire electrode being supported by the ends of the plurality of wireelectrode supporters, to which a high voltage is applied, so that atleast effective screen of the photoconductive layer is chargeduniformly, the electro-conductive layer serving as an opposed electrodeof the wire electrode.

Another aspect of the present invention embodies in a method forelectrophotographically manufacturing a screen of a CRT, the methodcomprising the steps of:

(1) firstly coating an inner surface of a panel faceplate to form avolatile conductive layer on the inner surface;

(2) secondly coating the volatile conductive layer with aphotoconductive solution to form a volatile photoconductive layer on thevolatile conductive layer, the photoconductive solution notcontaminating the volatile conductive layer;

(3) charging at least effective surface of the volatile photoconductivelayer with uniform electrostatic charges by pivoting a wire-type coronacharger along a first curvature corresponding to one of the curvaturesof the horizontal axis and the vertical axis of an interior surface ofthe panel faceplate over an entire interior surface of the panelfaceplate, the wire-type corona charger being pivoted with a spacingfrom the photoconductive layer, the wire-type corona charger generatinga corona discharge;

(4) exposing the volatile photoconductive layer through a shadow mask toa light according to a characteristic of the volatile photoconductivelayer, so as to selectively discharge the electrostatic charges havingbeen charged on the volatile photoconductive layer in step 3; and

(5) developing the photoconductive layer by attaching powdered particleson one of an exposed area and an unexposed are of the photoconductivelayer after charging the powdered particles, the exposed area havingbeen exposed to light in step 4 to lose the electrostatic charges,wherein the wire-type corona charger comprises:

at least three ground electrode plates, each of which hasarcuately-shaped upper edge with a curvature substantially equal to asecond curvature, the second curvature being a remaining one of thecurvatures of the horizontal axis and the vertical axis of the interiorsurface of the panel faceplate at each section of the panel faceplatenearest to each of the ground electrodes, the pair of ground electrodeplates being grounded with being arranged in parallel and spaced withregular intervals apart;

at least two sets of insulating blocks each of which is disposedrespectively between the ground electrode plates and made fromelectrically insulating material, each of the insulating blocks having aplurality of wire electrode supporters so arranged that their upper endsare arranged to have a curvature substantially equal to the secondcurvature; and

at least two wire electrodes being supported by the upper ends of thewire electrode supporters, to which a high voltage is applied, so thatat least effective screen of the photoconductive layer is chargeduniformly, the electro-conductive layer serving as an opposed electrodeof the wire electrodes.

A wire-type corona charger and a method using the charger according tothe present invention prevent generation of arc or spark and therebyenable the uniform charging by corona discharge on the photoconductivelayer without damaging the photoconductive layer even at repetitivecharging. Therefore, the present invention largely improves theefficiency of corona charging and as well makes the density or thethickness of the phosphor layer of the phosphor screen uniform.

BRIEF DESCRIPTION OF THE DRAWING

The above object, and other features and advantages of the presentinvention will become more apparent by describing in detail preferredembodiments thereof with reference to the attached drawings, in which:

FIG. 1 is a plan view partially in axial section of a color cathode-raytube;

FIG. 2 is a section of a screen assembly of the tube shown in FIG. 1;

FIGS. 3A through 3E are schematic sectional views for showing varioussteps in electro-photographically manufacturing the screen assembly ofthe tube according to the prior art, in which a portion of a faceplatehaving a conductive layer and an overlying photoconductive layertogether with devices used in each step is shown;

FIG. 4 is a schematic section of a conventional corona dischargeapparatus;

FIG. 5 is a perspective view of a conventional corona charger employedin the corona discharge apparatus of FIG. 5, the charging electrode ofwhich has a plurality of pin-type projections;

FIG. 6 is a perspective view of a wire-type corona charger forelectrophotographically manufacturing a screen of a CRT according to oneembodiment of the present invention;

FIG. 7 is a sectional view taken along the line 7—7 in FIG. 6;

FIG. 8 is an enlarged partial section taken along the line 8—8 in FIG.6;

FIG. 9 is a front view of an insulating block employed in the wire-typecorona charger of FIG. 6;

FIG. 10 is a front view of a ground electrode plate employed in thewire-type corona charger of FIG. 6;

FIG. 11 is a perspective view of another wire-type corona charger forelectrophotographically manufacturing a screen of a CRT according toanother embodiment of the present invention;

FIGS. 12 and 13 are graphs for showing distributions of the chargedvoltages according to the distance with respect to several chargingtimes, respectively when 4.5 KV and 5 KV are applied to the wire-typecorona charger;

FIGS. 14 and 15 are graphs for showing the ratio of the voltagevariances to the maximum voltages shown in FIGS. 12 and 13 under thesame conditions as those in FIGS. 12 and 13.

FIG. 16 is a graph for showing distributions of the charged voltagesaccording to the distance with respect to various values of the charginggap between the ground electrodes and the photoconductive layer, when4.5 KV is applied to the wire-type corona charger; and

FIG. 17 is a graph for showing ratio of the voltage variances to themaximum voltages shown in FIG. 16 under the same conditions as those inFIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, several embodiments of the present invention will bedescribed in detail with reference to the attached drawings.

FIG. 6 is a perspective view of a wire-type corona charger 100 forelectrophotographically manufacturing a screen of a CRT according to oneembodiment of the present invention, FIG. 7 is a sectional view takenalong the line 7—7 in FIG. 6, and FIG. 8 is an enlarged partial sectiontaken along the line 8—8 in FIG. 6. FIG. 9 is a front view of aninsulating block 105 employed in the wire-type corona charger 100 ofFIG. 6, and FIG. 10 is a front view of a ground electrode plate 103employed in the wire-type corona charger 100 of FIG. 6.

Referring to FIGS. 6 to 8, the wire-type corona charger 100 according tothe embodiment of the present invention comprises a pair of groundelectrode plates 103, a wire electrode 101, a pair of ground electrodeplates 103, and an insulating block 105.

The wire-type corona charger 100, installed in the corona dischargeapparatus 36 of FIG. 4 instead of the corona charger 50, is pivotedalong one of the curvatures of the horizontal axis and the vertical axisof the interior surface of the panel with spacings over the entireinterior surface of the panel, so as to uniformly charge at leasteffective surface of the photoconductive layer with a desired voltage.

Each arcuately-shaped upper edge of the pair of ground electrode plates103 has a curvature substantially equal to the remaining one of thecurvatures of the horizontal axis and the vertical axis of the interiorsurface of the panel. In case where the interior surface of thefaceplate 18 is aspheric, that is, the radiuses of the curvatures of thehorizontal and vertical axes of the interior surface of the panel aredifferent from each other, it is preferred that the above-mentionedremaining curvature has the longer radius, so as to enhance theuniformity of the charges and shortens the pivoting distance. Further,the pair of ground electrode plates 103 are arranged in parallel andspaced with regular intervals apart. The pair of ground electrode plates103 may be grounded, or a predetermined voltage such as 1 KV may beapplied to the pair of ground electrode plates 103, as is to thefocusing blade of U.S. Pat. No. 5,519,217.

The insulating block 105 is disposed between the pair of the groundelectrode plates 103 so as to insulate the pair of ground electrodeplates 103 and the wire electrode 101. the insulating block 105 and thepair of ground electrode plates 103 may be detachably assembled byassembling means 106, as shown in FIG. 6. In this case, slots 103′ maybe formed in one of the insulating block 105 and the pair of groundelectrode plates 103, so as to adjust the relative position of the wireelectrode 101 and the distal edge of the ground electrode plates 103. Inthe meantime, the insulating block 105 may be inserted in and formedintegrally with the pair of ground electrode plates 103 throughinjection molding without separate fixing means, differently from thatshown in FIG. 6.

The insulating block 105 has a plurality of wire electrode supporters102 and 102′ which support the wire electrode 101 on their ends. Thewire electrode supporters 102 and 102′ are arranged so that their endsare positioned along a curvature substantially equal to the aboveremaining curvature and lower than upper edges of the pair of groundelectrode plates 103. As shown in FIGS. 6 and 7, the wire electrodesupporters 102 and 102′ may be forcedly inserted in a supporter recess105′ formed on the upper surface of the insulating block 105. Otherwise,they may be inserted in the supporter recess 105′ by means of adhesives,or fixed by melting after insertion, or formed integrally with theinsulating block 105 by injection molding, etc.

As shown by two-dot-dashed line in FIG. 7, the pair of ground electrodeplates 103 may be formed integrally with each other by a base 103″. Alsoin this case, the insulating block 105 may be inserted onto the base103″ and then fixed by a fixing means including adhesives, or be formedintegrally therewith. Preferably, the upper surface of the insulatingblock 105 as above may be so formed to prevent leakage of high voltage.

More preferably, the wire electrode supporters 102′ disposed at theopposite ends among the wire electrode supporters 102 and 102′ maysupport the wire electrode 101 in such a manner that even the peripheralportions of the effective viewing screen of the faceplate 18 can beuniformly charged. In case where the wire electrode supporters 102 and102′ are supported in the supporter recess 105′ after being insertedthereinto, it is preferred that the upper surface of the insulatingblock 105 is formed to have a curvature substantially equal to theremaining curvature, and that the plurality of wire electrode supporters102 excepting from those at the opposite ends extend in normaldirections with respect to the curvature of the upper surface of theinsulating block 105, while the wire electrode supporter 102′ at theopposite ends extend to be open as widely as possible outward from thenormal directions.

As apparent from the following description in relation to FIGS. 12 to17, the value of the contact resistance due top the contact between thewire electrode 101 and the wire electrode supporters 102 and 102′ has alarge effect on the corona discharge. Therefore, required is a selectionof material which exhibits high strength and mall current loss even withsmall contact area, in order to minimize the contact resistance. Thepresent invention employs a material such as glass and ceramic, whichnot only shows the above characteristic but also has a high dielectricconstant and durability, thereby further improving the uniformity ofcharge and the efficiency of corona charging. Furthermore, in order toachieve the same objects as above, the distal ends of the wire electrodesupporters 102 and 102′ may be formed sharply, e.g., their sections inthe curvature direction may respectively have an inverted V-shape, so asto minimize the contact area between the wire electrode 101 and the wireelectrode supporters 102 and 102′, thereby minimizing the leakage ofhigh voltage.

Therefore, the wire electrode 101 can have a desired curvature becauseit is supported on the distal ends of the wire electrode supporters 102and 102′ as constructed above. By applying high voltage to the wireelectrode 101, at least effective screen of the photoconductive layer 34can be charged uniformly as described later on.

In the meantime, the wire electrode 101 has a tension-applying means101′ for applying tension to the wire electrode 101. Referring to FIGS.6 and 8, the tension-applying means 101′ located at either ends of theinsulating block 105 is formed integrally with the opposite ends of thewire electrode 101. The wire electrode 101 is supported on theinsulating block 105 by means of tension-support means 107 at one pointbetween the tension-applying means 101′ and the wire electrodesupporters 102′. Therefore, a constant tension is continuously appliedto the wire electrode 101 along its entire length after the wireelectrode 101 is installed, to thereby enable the uniform coronadischarge along the entire length of the wire electrode 101.

Preferably, the wire electrode 101 may be made of tungsten plated withgold, to further improve the discharge efficiency.

In addition, the wire electrode 101 may be located lower than the distaledge of the pair of ground electrode plates 103 by a depth Hcorresponding to a half of the spacing W between the pair of groundelectrode plates 103, and located at the middle of the spacing, therebygenerating symmetric corona discharge to enable further uniformcharging. In the tested wire electrode 101 whose testing result is shownin FIGS. 12 to 17, the spacing W is 12.8 mm and the depth H is 6 mm.

FIGS. 12 to 17 show several results after the above-mentioned chargingstep performed by the wire-type corona charger 100 according to oneembodiment of the present invention. FIGS. 12 and 13 are graphs forshowing distributions of the charged voltages according to the distancewith respect to several charging times, respectively when 4.5 KV and 5DK are applied to the wire electrode 101. FIGS. 14 and 15 are graphs forshowing ratio of the voltage variances to the maximum voltages shown inFIGS. 12 and 13 under the same conditions as those in FIGS. 12 and 13.FIG. 16 is a graph for showing distributions of the charged voltagesaccording to the distance with respect to various values of the charginggap between the ground electrode plates 103 and the photoconductivelayer 34, when 4.5 KV is applied to the wire electrode 101. FIG. 17 is agraph for showing ratio of the voltage variances to the maximum voltagesshown in FIG. 16 under the same conditions as those in FIG. 16.

Throughout FIGS. 12 to 17, the maximum charged point is located at thepositions of the wire electrode supporters 102 and 102′. Referring toFIGS. 12 to 15, in order to achieve uniform charging, it is necessary tobe charged for about 8 seconds when the voltage applied to the wireelectrode 101 is 4.5 KV, and only for 3 to 5 seconds when 5 KV, thecharged voltage has substantially uniform value between 300 and 400volt.

Referring to FIGS. 16 to 17, it is proper for the charging gap to be inthe range from 4 to 9 mm in order to achieve uniform charging, when thevoltage applied to the wire electrode 101 is 4.5 KV.

In general, cables for applying high voltage to the wire electrode 101may be connected directly to the opposite ends of the wire electrode101. However, it is preferred that the cable 110 may be fixedly insertedin a cable groove 105 a formed in the insulating block 105 to preventleakage of high voltage, as shown in FIG. 8.

FIGS. 8 and 9 show the cable groove 105 a formed to be exposed on oneside surface of the insulating block 105 in consideration of thethickness and manufacture of the insulating block 105. In this case, itis preferred that insulating plates 104 are located between the groundelectrode plates 103 and the exposed side surfaces of the insulatingblock 105 as shown in FIGS. 6, 7, and 10, so as to prevent leakage ofvoltage from the cable 110 inserted in the cable groove 105 a.

FIG. 11 is a perspective view of a wire-type corona charger 200 forelectrophotographically manufacturing a screen of a CRT according toanother embodiment of the present invention.

The wire-type corona charger 200 includes at least three groundelectrode plates 203, at least two insulating blocks 205, and at leasttwo wire electrodes 201.

Similarly with the wire electrode 101 in FIG. 6, the wire electrodes 201are supported by at least two sets of wire electrode supporters 202 and202′ arranged on the insulating blocks 205. Besides, not only theconstructions and functions of the ground electrode plates 203, theinsulating blocks 205, and the wire electrodes 201 but other conditionsare similar to those in the previous embodiment.

The wire-type corona charger 200 having the above-described constructionmay be installed over the entire faceplate 18 as those in U.S. Pat. No.5,519,217. Then, the wire-type corona charger 200 can uniformly chargethe entire faceplate 18 when it travels a distance corresponding to aspacing between two adjacent wire electrodes 201. Therefore, thewire-type corona charger 200 can more rapidly perform the chargingprocess in comparison with the wire-type corona charger 100. Moreover,though the wire-type corona charger 200 is not installed over the entirefaceplate 18, a desired quantity of charges can be obtained even by lowvoltage because only one-time turning of the wire electrodes 201corresponds to plural-time turnings of the wire-type corona charger 100in FIG. 6. In addition, the quantity of charges at the periphery of theeffective screen of the panel 12 can be regulated by changing thevoltage applied to the wire electrodes 201.

Preferably, the wire electrode supporters 202 and 202′ are arranged in acrossed alignment set by set. That is, the wire electrode supporters 202and 202′ are arranged in line along every other sets but not betweenadjacent sets, so as to maximize the charging uniformity by compensatingthe reduction of charges due to the leakage of charges through the wireelectrode supporters 202 and 202′.

Hereinafter, described will be a method for electrophotographicallymanufacturing a screen of a CRT using the wire-type corona charger 100shown in FIG. 6, referring again to FIG. 3.

The method comprises the steps of: (1) firstly coating an inner surfaceof the panel for form a volatile conductive layer 32 on the innersurface; (2) secondly coating the volatile conductive layer 32 withphotoconductive solution to form a volatile photoconductive layer 34 onthe volatile conductive layer 32, the photoconductive solution notcontaminating the conductive layer 32; (3) charging at least effectivesurface of the volatile photoconductive layer 34 with uniformelectrostatic charges by pivoting a corona charger along one of thecurvatures of the horizontal axis and the vertical axis of an interiorsurface of the panel with intervals over the entire interior surface ofthe panel, the corona charger generating a corona discharge; (4)exposing the volatile photoconductive layer 34 through a shadow mask toa light according to a characteristic of the volatile photoconductivelayer 34, so as to selectively discharge the electrostatic chargeshaving been charged on the volatile photoconductive layer 34 in step 3;and (5) developing the photoconductive layer 34 by attaching powderedparticles on one of an exposed area and an unexposed area of thephotoconductive layer 34 after charging the powdered particles, theexposed area having been exposed to light in step 4 to lose theelectrostatic charges.

The powdered particles may be one of the first to the third phosphorparticles, and the steps 3 to 5 may be repeatedly performed with respectto the other particles. Also, the light-absorptive material of the blackmatrix may be formed as above, and in this case, the method furthercomprises, before the charging step 4, the steps of: charging thephotoconductive layer 34 with uniform electrostatic charges by coronadischarge in order to develop the light-absorptive material, exposingthe photoconductive layer 34 through a shadow mask to a light accordingto a characteristic of the photoconductive layer 34, so as toselectively discharge the electrostatic charges charged on thephotoconductive layer 34; and developing the photoconductive layer 34 byattaching light-absorptive material on one of an exposed area and aunexposed area of the photoconductive layer 34 after charging thelight-absorptive material, the exposed area being exposed to light inthe exposing step to lose the electrostatic charges. In this case, thelight-absorptive material is formed in a predetermined matrixconstruction.

In the above charging step, the charging apparatus as disclosed in U.S.Pat. No. 5,132,188 or U.S. Pat. No. 5,519,217 may be employed. Further,the high voltage applied to the wire electrodes 101 and 201 may beincreased in proportion to the increase of the gap between thephotoconductive layer 34 and the wire electrode 101, the reduction ofthe thickness of the photoconductive layer 34, and the increase of thepivoting speed of the wire-type corona charger, to thereby enable toregulate the quantity of the electrostatic charges on thephotoconductive layer 34 by the wire electrode 101 in the charging step.It is preferred for the following process that the photoconductive layer34 is charged with uniform electrostatic charges between 300 and 400volt. As is in the detailed description with reference to FIGS. 12 to17, the gap between the ground electrode plates 103 and thephotoconductive layer 34 is preferably more than 3 mm.

Also, the photoconductive layer 34 may include a material responsive toone of the visible rays and the ultraviolet rays in the secondly coatingstep, so that the photoconductive layer 34 is exposed to light of thevisible rays or the ultraviolet rays according to the material of thephotoconductive layer 34 in the exposing step. The solution for thephotoconductive layer 34 responsive to the ultraviolet rays, forexample, may contain: an electron donor material, such as about 0.01 to10 percent by weight of bis-1,4-dimethyl phenyl (-1,4-diphenyl(butariene) or 2 to 5 percent by weight of tetrapheyl ethylene; anelectron acceptor material, such as about 0.01 to 10 percent by weightof at least one of trinitro-fluorenone and ethyl anthraquinone; amacro-molecular binder, such as 1 to 30 percent by weight polystyrene;and a solvent, such as the remaining percent by weight of toluene orxylene. This solution is further preferable because it does not requirethe dark environment for the exposing step.

Moreover, in the developing step, instead of being charged by thecontact as shown in FIG. 3D, the powdered particles may be charged by acontact with a pipe in the course of being supplied, or charged by acorona discharge just before being sprayed by a spray coater.

The fixing step as shown in FIG. 3E may employ a vapor swelling methodwherein the fixing is performed by a contact with a solvent vapor suchas acetone and methyl isobutyl ketone, or a spraying method wherein anelectrostatic solution spray gun sprays a mixture of at two kinds amongmethyl isobutyl ketone, TCE, toluene, and xylene of the petrolium groupon the developed powdered-particles of red, green, and blue. Otherwise,the fixing step may omitted partly or totally.

In addition, the pivoting speed of the charger and the voltage-applyingtime and the applied voltage to each wire electrode may be variableindependently to or in combination with each other, so as to charge theentire effective screen of the panel faceplate 18 to a uniformpredetermined voltage. That is, the wire electrodes 101 and 201 as shownin FIGS. 6 and 11 may be pivoted slowly at the periphery of the screen,or the charging time at the wire electrodes may be gradually prolongedas it goes inward from those at the sides, at the beginning and closingof the charging step. Further, the voltage applied to the wireelectrodes may be changed from the higher voltage than to the samevoltage as that applied to the other wire electrodes, so that theperiphery of the faceplate may be charged equally to the other partsthereof.

As apparent from the above description of the construction and functionof the wire-type corona charger and the method forelectrophotographically manufacturing a screen of a CRT using thewire-type corona charger according to several embodiments of the presentinvention, the wire-type corona charger for electrophotographicallymanufacturing a screen of a CRT is achieved basically by means of thewire electrodes 101 and 201 and the wire electrode supporters 102 and102′, wherein the wire electrodes 101 and 201 enables more rapid anduniform charging of the photoconductive layer in the charging step ofthe process for electrophotographically manufacturing a screen of a CRT.The present invention further enables a uniform exposure and developmentin the above exposing and developing steps, thereby not only improvingthe productivity and quality of the CRT but also increasing the chargingefficiency.

While the present invention has been particularly shown and describedwith reference to the particular embodiments thereof, it will beunderstood by those skilled in the art that various changes in form anddetails may be effected therein without departing from the spirit andscope of the invention as defined by the appended claims.

What is claimed is:
 1. A wire-type corona charger forelectrophotographically manufacturing a screen of a CRT, the wire-typecorona charger being installed in a corona discharge apparatus andpivoted with a spacing over an entire interior surface of a panelfaceplate of the screen along a first curvature which is one ofcurvatures of a horizontal axis and a vertical axis of the interiorsurface of the panel faceplate, so as to uniformly charge at leasteffective surface of a photoconductive layer with a desired voltage, thephotoconductive layer being formed on an electro-conductive layer formedon the interior surface of the panel faceplate, the wire-type coronacharger comprising: a pair of ground electrode plates each of which hasarcuately-shaped upper edge with a curvature substantially equal to asecond curvature, the second curvature being a remaining one of thecurvatures of the horizontal axis and the vertical axis of the interiorsurface of the panel faceplate, the pair of ground electrode platesbeing grounded with being arranged in parallel and spaced with regularintervals apart; an insulating block disposed between the pair of theground electrode plates and made from electrically insulating material,the insulating block having a plurality of wire electrode supporters soarranged that their upper ends are arranged to have a curvaturesubstantially equal to the second curvature and lower than upper edgesof the pair of ground electrode plates; and a wire electrode beingsupported by the upper ends of the plurality of wire electrodesupporters, to which a high voltage is applied, so that at leasteffective screen of the photoconductive layer is charged uniformly.
 2. Awire-type corona charger as claimed in claim 1, wherein the upper endsof the wire electrode supporters are formed sharply, so that theirsections in a direction of the second curvature respectively have aninverted V-shape, so as to minimize a contact area between the wireelectrode and the wire electrode supporters, thereby minimizing leakageof high voltage.
 3. A wire-type corona charger as claimed in claim 1,further comprising tension-applying means for applying tension to thewire electrode, so as to generate a uniform corona discharge along anentire length of the wire electrode.
 4. A wire-type corona charger asclaimed in claim 3, wherein the tension-applying means are located ateither ends of the insulating block and formed integrally with oppositeends of the wire electrode, further comprising a pair of tension-supportmeans each of which supports the wire electrode at either points betweenthe tension-applying means and the wire electrode supporters disposed ateither ends thereof, so that a constant tension is continuously appliedto the wire electrode along its entire length after the wire electrodeis installed.
 5. A wire-type corona charger as claimed in claim 1,wherein end supporters among the wire electrode supporters, which aredisposed at the opposite ends, support the wire electrode in such amanner that even peripheral portions of an effective screen of the panelfaceplate can be uniformly charged.
 6. A wire-type corona charger asclaimed in claim 1, wherein the wire electrode supporters are fixedlyinserted in a supporter recess formed on an upper surface of theinsulating block.
 7. A wire-type corona charger as claimed in claim 6,wherein a upper surface of the insulating block is formed to have acurvature substantially equal to the second curvature, and interiorsupporters of the wire electrode supporters extend in normal directionwith respect to the curvature of the upper surface of the insulatingblock, while end supporters of the wire electrode supporters extend tobe open as widely as possible outward from the normal directions, theend supporters being disposed at the opposite ends of the wire electrodesupporters and the interior supporters being the remaining wireelectrode supporters excepting from the end supporters.
 8. A wire-typecorona charger as claimed in claim 1, wherein the wire electrode is madeof tungsten plated with gold.
 9. A wire-type corona charger as claimedin claim 1, wherein the wire electrode is located at a center of agap(W) between the ground electrode plates with being lower than thearcuately-shaped upper edge of the ground electrode plates by a depth Hcorresponding to a half of the gap.
 10. A wire-type corona charger asclaimed in claim 1, wherein the insulating block and the pair of groundelectrode plates may be detachably assembled by assembling means throughholes thereof, the hole(s) in one of the insulating block and the pairof ground electrode plates being slotted so as to adjust a relativeposition of the wire electrode and the arcuately-shaped upper edge ofthe ground electrode plates.
 11. A wire-type corona charger as claimedin claim 1, wherein a cable for applying a high voltage to the wireelectrode is fixedly inserted in a cable groove formed in one of twoexposed side surfaces of the insulating block, and at least oneinsulating plate is located between the ground electrode plate disposedon the one exposed side surface and the one exposed side surface of theinsulating block to cover the cable groove, so as to prevent leakage ofvoltage from the cable to the ground electrode plates.
 12. A wire-typecorona charger as claimed in claim 1, wherein the interior surface ofthe panel faceplate is aspheric, and the second curvature has a longerradius than the first curvature.
 13. A wire-type corona charger asclaimed in claim 1, wherein the insulating block is inserted in andformed integrally with the ground electrode plates without separatefixing means.
 14. A wire-type corona charger as claimed in claim 1,wherein the ground electrode plates comprise a base in a body, and theinsulating block is inserted onto the base and then fixed by a fixingmeans including adhesives, and the insulating block is formed integrallywith the base and the ground electrode plates by molding.
 15. Awire-type corona charger for electrophotographically manufacturing ascreen of a CRT, the wire-type corona charger being installed in acorona discharge apparatus and pivoted to a predetermined distance alonga first curvature which is one of curvatures of a horizontal axis and avertical axis of the interior surface of the panel faceplate, so as touniformly charge at least effective surface of a photoconductive layerwith a desired voltage, the photoconductive layer being formed on anelectro-conductive layer formed on the interior surface of the panelfaceplate, the wire-type corona charger being pivoted with a spacingfrom the photoconductive layer, the wire-type corona charger comprising:at least three ground electrode plates, each of which hasarcuately-shaped upper edge with a curvature substantially equal to asecond curvature, the second curvature being a remaining one of thecurvatures of the horizontal axis and the vertical axis of the interiorsurface of the panel faceplate at each section of the panel faceplatenearest to each of the ground electrodes, the pair of ground electrodeplates being grounded with being arranged in parallel and spaced withregular intervals apart; at least two sets of insulating blocks each ofwhich is disposed respectively between the ground electrode plates andmade from electrically insulating material, each of the insulatingblocks having a plurality of wire electrode supporters so arranged thattheir upper ends are arranged to have a curvature substantially equal tothe second curvature; and at least two wire electrodes being supportedby the upper ends of the wire electrode supporters, to which a highvoltage is applied, so that at least effective screen of thephotoconductive layer is charged uniformly.
 16. A wire-type coronacharger as claimed in claim 15, wherein the wire electrode supportersare arranged in a crossed alignment set by set.
 17. A wire-type coronacharger as claimed in claim 15, wherein the wire electrodes areinstalled over the entire faceplate and pivoted with a distancecorresponding to a gap between two adjacent wire electrodes, therebyuniformly charging the entire faceplate.
 18. A wire-type corona chargeras claimed in claim 15, wherein the upper ends of the wire electrodesupporters are formed sharply, so that their sections in a direction ofthe second curvature respectively have an inverted V-shape, so as tominimize a contact area between the wire electrodes and the wireelectrode supporters, thereby minimizing leakage of high voltage.
 19. Awire-type corona charger as claimed in claim 15, further comprisingtension-applying means for applying tension to the wire electrodes, soas to generate a uniform corona discharge along entire lengths of thewire electrodes.
 20. A wire-type corona charger as claimed in claim 19,wherein the tension-applying means are located at either ends of each ofthe insulting block and formed integrally with opposite ends of each ofthe wire electrode, each set of insulating blocks further comprising apair of tension-support means each of which supports the wire electrodeat either points between the tension-applying means and the wireelectrode supporters disposed at either ends thereof, so that a constanttension is continuously applied to each of the wire electrodes along itsentire length after each of the wire electrodes is installed.
 21. Awire-type corona charger as claimed in claim 15, wherein end supportersof the wire electrode supporters, which are disposed at the oppositeends, support the wire electrode in such a manner that even peripheralportions of an effective screen of the panel faceplate can be uniformlycharged.
 22. A wire-type corona charger as claimed in claim 15, whereinthe wire electrode supporters are fixedly inserted in supporter recessesformed on upper surfaces of the insulating blocks.
 23. A wire-typecorona charger as claimed in claim 22, wherein an upper surface of eachof the insulating blocks is formed to have a curvature substantiallyequal to the second curvature, and interior supporters of the wireelectrode supporters extend in normal directions with respect thecurvature of the upper surface of each of the insulating blocks, whileend supporters of the wire electrode supporters extend to be open aswidely as possible outward from the normal directions, the endsupporters being disposed at the opposite ends of the wire electrodesupporters and the interior supporters being the remaining wireelectrode supporters excepting from the end supporters.
 24. A wire-typecorona charger as claimed in claim 15, wherein the wire electrodes aremade of tungsten plated with gold.
 25. A wire-type corona charger asclaimed in claim 15, wherein each of the wire electrodes is located at acenter of a gap between two adjacent ones of the ground electrode plateswith being lower than the arcuately-shaped upper edge of said twoadjacent ones by a depth H corresponding to a half of the gap.
 26. Awire-type corona charger as claimed in claim 15, wherein a cable forapplying a high voltage to each of the wire electrodes is fixedlyinserted in a cable groove formed respectively in one of two exposedside surfaces of each of the insulating blocks, and at least oneinsulating plate is located between the ground electrode plate disposedon the one exposed side surface and the one exposed side surface of eachof the insulating blocks to cover each of the cable grooves, so as toprevent leakage of voltage from the cable to the ground electrodeplates.